1. Technical Field
This invention relates to testing and qualification of panel products and more specifically to the panel products destined to be used under shear stress such as wood I-joist web members or similar applications in which the shear strength of the panel materials is an important design parameter.
2. Importance of the Invention and Prior Art
Particleboard panel products are manufactured by producing a flow of wood pieces of varying dimension ranging in size from wood dust to large flakes or strands, mixing with a resin-wax binding agent and followed by forming a mat of the wood particle—resin—wax mix and placing the mat in a press where the resin is cured under heat and pressure thereby binding the particles together and forming a useful panel product. A wide variation in wood particle type and resin content is used and therefore a wide variation in physical properties of the panel products is available for various applications. When such a panel is to be used for a structural application it is essential that the characteristics of the wood particles, resin, wax and pressing time and temperature be controlled so that the desired properties emerge in the finished goods. For enhanced properties the wood is prepared in strands cut along the grain direction of the wood, and the strands are oriented in a preferred direction in the process of forming the mat before it goes into the press.
Plywood may be manufactured using a wide variety of wood veneer species and grades, and varying in the number of plies, thickness of the wood veneer, as well as resin and pressing time and temperature. If plywood is to be used in a shear loading configuration it is important to know the shear strength in plywood.
For the manufacturer of the wood I joist product, web material may be purchased from a variety of sources and it is essential to the integrity of the I-joist product that the panel products meet requirements for durability, thickness and shear strength. Because the wood I-joist is replacing the wide solid-sawn wood joist in much residential and light commercial construction, it is important to public safety that these materials be properly tested in an on-going quality control program.
ASTM D5055 “Standard Specification for Establishing and Monitoring Structural Capacities of Prefabricated Wood I-Joists” refers to ASTM D1037 in respect of shear strength in the web members of the composite wood I-joist. Therefore the need is established for an accurate testing machine that will perform the required testing. With increasing volume of these products going into construction, a test that requires a minimum of labor input is also very desirable.
With panel products manufactured as plywood or particleboard being used more extensively as web members in a wood “I” joist configuration it is imperative that the horizontal shear strength of these panel products be verified and properly characterized so that the design of these wood I-joist products will perform as bending members in structural service.